1. Field of the Invention
This invention relates to a photogravure plate making method capable of performing a quite excellent photogravure plating under application of a positive-type thermal resist including a requisite and sufficient developing latitude through non-heating operation after forming a coating film.
2. Description of the Related Art
The prior art traditional positive-type photosensitive lithography plate contains novolac resin and o-quinonediazide composition, a substance photosensitive to white light, this plate becomes a ketene structure while producing an Armdt-Eistert type transition through pholysis (chemical change) of o-quinonediazide as indicated in a chemical formula (1) as follows, produces five-membered ring carboxylic acid, ketene at an upper part of photosensitive layer at an exposed portion is reacted with naphthoquinonediazide at the lower part of the photosensitive layer to form lactone, this becomes sodium carboxylic acid while lactone ring is opened when a developing action occurs with alkaline aqueous solution, the coexisting novolac resin also shows elution because it is resoluble with alkali and in turn, the photosensitive layer non-yet exposed portion produces a coupling reaction together with the coexisting novolac resin, it becomes an alkali-resolution retardant and left as a resist image. In this way, if it includes o-quinonediazide composition, a substantial developing latitude can be attained.
In this case, the developing latitude can be defined as one in which a developing operation can be carried out while there is a difference between a time until the exposed portion is exposed to the developing liquid and the exposed portion is completely removed and a time in which a residual film rate at the non-exposed portion is sufficiently assured even if it is exposed to the developing liquid. 
To the contrary, in order to enable a photogravure plate making to be carried out even under white light lamp, a positive-type photosensitive composition utilizing a change other than a chemical change has been invented, there has been devised to provide a method for printing a positive image with a laser light of infrared wave length region, increasing a solubility of the exposed portion against the developer liquid to form a positive image and thus this has been carried out through an offset plate making or a flexographic plate making. As the technical documents; there have been provided the gazettes of Japanese Patent Laid-open Numbers 1998(10)-268,512; 1999(11)-194,504; 1999(11)-223,936; 1999(11)-84,657; 1999(11)-174,681; 1999(11)-231,515; WO97/39,894; WO98/42,507; the gazettes of Japanese Patent Laid-Open Numbers 2002-189293; and 2002-189,295 and the like.
The positive-type photosensitive lithography plate described in each of the aforesaid documents has, as its major photosensitive component, substance absorbing infrared ray such as infrared absorbing pigment to convert it into heat and alkaline soluble resin such as novolac resin and the like, and a physical change such as conformation change of resin and the like is generated by heat produced by an infrared laser light exposed light and then solubility against developer liquid is increased.
However, the positive-type photosensitive lithography plate not containing o-quinonediazide composition, printing a positive image with a laser beam in an infrared wavelength range, producing a physical change such as conformation change of resin and the like to increase its solubility requires at present a burning process (a heating operation) after coating a film. Even if the burning process is carried out, a difference in dissolution speed between an exposed part and a non-exposed part is low, basic performances of a printing plate such as sensitivity and developing latitude are poor, so that it is hard to satisfy a stability in developing process when the number of plates for developing process is increased.
In regard to the aforesaid situation, this circumstance is quite different in the photogravure plate making process. In Japan where the photogravure plate making and printing technology has been mostly distributed in the industry, a photogravure plate making method capable of carrying out the photogravure plate making under application of positive-type thermal resist enabling a developing process to be performed under no heating after forming a coated film has not been performed in the prior art at all and there are no patent documents and experiment documents at all.
The photogravure plate making process for a plate-made roll through a corrosive/laser beam plate making method is comprised of loading→degreasing→washing→pickling→washing→ballade processing→washing→balladecopperplating→washing→grinding with a grind stone→washing→coating of photosensitive agent→coating of antioxidant→image printing with infrared laser exposure device→developing→washing→etching→washing→resist peeling→washing→grinding→washing →unloading.
As technical documents disclosing the photogravure plate making process for a gravure plated roll by a corrosive/laser plate making process, some prior art documents can be cited, i.e. Japanese Patent Application Numbers 1998(10)-193551; 1998(10)-193552; Japanese Patent Laid-Open Numbers 2000-062342; 2000-062343; 2000-062344; 2001-179923; 2001-179924; 2001-187440; 2001-187441; 2001-191475; 2001-191476; 2001-260304; 2002-127369; 2002-187249; 2002-187250; 2002-200728; 2002-200729; 2002-307640; and 2002-307641.
All the photogravure plate making processes described in the aforesaid documents are carried out such that a photosensitive film composed of negative-type photosensitive composition agent is coated and the photosensitive film composed of positive-type photosensitive composition agent is not coated. In the prior art etching process, the negative-type photosensitive film is coated on the gravure-plated roll, the coated film is dried and solidified at a room temperature to form the negative-type photosensitive film, a printing is carried out with argon ion laser beam, and the prior art does not form a positive-type photosensitive film on the gravure-plated roll and does not perform a printing of the positive-type photosensitive agent image with a laser beam of infrared wave length.
A high-power semiconductor laser head manufactured by Creo-Scitex Corporation of Canada radiates a laser of infrared wavelength range, and this is installed at an offset printing machine to perform radiation against the positive-type photosensitive composition, a superior developing can be carried out and so this is practically operated in a world-wide basis.
When a beam diameter of argon ion laser beam and a beam diameter of laser beam with a wavelength of 700 to 1,100 nm are the same value to each other, a resolution of laser at the positive-type photosensitive composition is higher than that at the negative-type photosensitive composition and its processing time can be substantially reduced.
Further, a more superior clear pattern can be attained by the photosensitive film of positive-type photosensitive composition used for printing a negative image with argon ion laser rather than by the photosensitive film of negative-type photosensitive composition used for printing a negative image with argon ion laser. This is caused by a difference in clearness in pattern under a difference in the positive-type photosensitive composition and the negative-type photosensitive composition.
A reason why the positive-type photosensitive composition agent is used for the offset plate making or flexographic plate making in the prior art, but as not been used in the photogravure plate making consists in the fact that the negative-type photosensitive agent could be used in the late photogravure plate making. The negative-type photosensitive agent is material for use in radiating ultraviolet rays to fix a degree of polymerization of resin at the exposed portion, so that whatever material quality at the coated surface may be selected, a requisite and sufficient developing latitude can be assured.
In turn, the positive-type photosensitive composition agent having a developing latitude capable of being satisfied in relation with a copper sulfate plating at the photogravure printing roll was not present at all. In particular, because the photosensitive composition agent not performing any burning after coating was not present at all. Even if the positive-type photosensitive composition agent used in either the offset plate making or flexographic plate making is coated on the gravure-plated roll, a condition capable of forming film is scarcely present. In many cases, the coating film of the positive-type photosensitive composition agent for the photogravure plated roll is entirely flowed by the alkaline developing agent. This is similarly applied even in the case that the burning is carried out after coating.
A photogravure plate making system of high resolving power using the positive-type photosensitive film under application of either a semiconductor laser or YAG laser or the like capable of highly outputting a laser beam of infrared wavelength range is highly desired for its realization in reference to a small-sized device, an environmental light at the time of plate making operation, a resolving power and a clear pattern and the like as compared with the case in which an argon ion laser is used.
The present inventors et al. have started to develop the positive-type photosensitive composition agent having a requisite and sufficient developing latitude without performing any burning after coating in relation with the copper sulfate plating of a photogravure printing roll in view of the aforesaid circumstances.
Then, the present inventors et al. have made undiluted solution of the positive-type photosensitive composition mixed with novolac resin and cyanine pigment in reference to the etching process applied as one of the plate making methods for a photogravure printing roll and coated the positive-type photosensitive agent thinned by the solvent to the copper sulfate plating surface of the photogravure plated roll to form it. In the case of coating of the positive-type photosensitive agent, a photosensitive film coating device according to Japanese Kokoku Publication No. 1995 (07)-109511 (manufactured by Think Laboratory Co., Ltd.) was used. Then, a laser of infrared wavelength range was radiated by an infrared laser exposing device (manufactured by Think Laboratory Co., Ltd.) having a high output semiconductor laser head of Creo-Scitex Corporation mounted therein to print the positive image, a developing test was carried out, resulting in that the photosensitive film was entirely removed and a satisfactory resist image could not be attained at all.
Evaluation of a formed film made by the photosensitive film coating device in accordance with Japanese Kokoku Publication No. 1995 (07)-109511 showed that this prior art device is a spiral scanning system of contact coating type where the coating roll is immersed in the photosensitive agent in the tank, the photosensitive agent is coated by several times against the coated surface and it can be assumed that air is mixed with the photosensitive film, the tank is an opened structure, so that solvent in the photosensitive agent stored in the tank is evaporated to remove evaporating latent heat, the coating roll is cooled to generate a coating of whitening phenomenon, a concentration of the solvent is always decreased, viscosity is gradually increased and a coated film of uniform film thickness cannot be attained. As a result, the present inventors have concluded that the positive-type photosensitive agent film is quite improper even if the negative-type photosensitive agent is properly coated and the photosensitive film coating device according to Japanese Kokoku Publication No. 1995 (07)-109511 makes a film.
In view of the foregoing, the present inventors have replaced with the photosensitive film coating device according to Japanese Kokoku Publication No. 1995 (07)-109511 and developed a photosensitive film coating device in which the solvent in the photosensitive agent in the tank is not evaporated in its sealingly closed state, the material can be coated on the gravure plated roll under no contacted state, and the coating accompanying with the whitening phenomenon can be avoided.
The photosensitive film coating device will be described in detail in the column of the preferred embodiment of the present invention.
In brief, as a method for coating the positive-type photosensitive agent to a gravure plated roll, the upper end of the photosensitive agent flowing-out pipe acting as a vertical pipe is approached to a lower surface of one end of the gravure plated roll chucked at both ends in a horizontal state and rotated, the photosensitive agent is supplied to overflow while being slightly bulged out at the upper end of the photosensitive agent flowing-out pipe, the photosensitive agent flowing-out pipe is moved from one end of the gravure plated roll to the other end thereof, the coating liquid is coated on the gravure plated roll by a spiral scanning system and the rotation of the roll is continued until the coated film shows an automatic drying.
In view of the foregoing, our continued study showed that a strong close contacted state of the positive-type photosensitive composition against the copper sulfate plated surface could not be attained and its developing operation caused the positive-type photosensitive composition to be rapidly eliminated with alkaline developing liquid for all the image lines and non-image lines.
Due to this fact, it could not be avoided that the burning operation for heating the film surface up to a high temperature after film coating is carried out and a close contacting force is applied.
A reason why it was necessary to perform the burning operation consisted in the fact that a film is not formed due to a quite poor close fitness of the positive-type photosensitive composition against the copper sulfate plating surface and the burning operation after film forming enables a hydrogen bond of alkaline soluble organic high molecular substance having a phenolic hydroxyl group to be increased and a close fitness to be improved.
Our continued study under an assumption that the burning operation is carried out at present showed that the positive-type photosensitive composition having the aforesaid manufactured novolac resin and cyanine pigment mixed to each other was coated on the gravure plated roll, the burning was carried out for 30 minutes to cause a film surface temperature to become 60° C., it was exposed with laser and developed, resulting in that a poor developed state was attained.
Thus, burning was carried out for 30 minutes in such a way that the film surface temperature becomes 130° C. Even under this state, a poor phenomenon occurred in which the image line as well as non-image line is entirely removed.
The present inventors concluded that a cause for producing a poor developed state even under performing the burning operation consisted in a too lower close fitness of the positive-type photosensitive composition against the copper sulfate plating.
Thus, as a result of increasing a close fitness force at the photosensitive film through inputting silane coupling adent as promoter for increasing a close fitness force to the positive-type photosensitive composition, both exposure and developing could be carried out in a little superior manner.
More practically, the gravure plated roll with a diameter of φ200 mm, for example, was rotated at a low speed of 25 r.p.m., the positive-type photosensitive agent was coated on it, its rotation was continued not to cause any liquid dripping, the photosensitive film having a degree of dry where the solvent is gasified to a state in which no liquid dripping occurs upon elapsing by 5 minutes under a natural drying condition was set, and after this operation, a residual concentration of solvent upon burning at 130° C. for 30 minutes was lower than 2%, the image could be printed by a laser and its developing operation could be carried out.
However, a close fitness against the film could be said as the best one and both exposure and developing did not exceed a little bit superior range.
In addition, it became apparent that when the film surface temperature was set to 130° C., the burning and its subsequent cooling required a time more than 100 minutes, a large amount of heat energy was required, its running cost was high and it showed a poor practical characteristic.
Additionally, when the film surface temperature was set to 130° C., hydrogen bond of alkaline soluble organic high molecular substance having a phenolic hydroxyl group was strengthened to cause a developing to be hardly carried out and at the same time, it was sensed from a poor clearness of pattern that cyanine pigment was denatured and its sensitivity was lowered.
Then, a superior observation about the resist image made it apparent that many pinholes were generated. In the case of the negative resist image, such pinholes as above were not produced. Reasons in regard to these phenomena consisted in the facts that a mere washing with water after precision grinding by a grinder stone did not enable ground powder adhered to the gravure plated roll to be completely washed away; if the plate making room was not made as a clean room of high degree, the powder dusts were adhered to the gravure plated roll during its transporting operation; and the positive resist image was more quite sensitive to the film making condition than that of the negative resist image.
Thus, occurrence of pinholes could be restricted by applying an sufficient wiping-off operation with a wiping cloth before coating the photosensitive agent to the gravure plated roll in reference to our various kinds of studying.
Next, the present inventors et al. have considered it important that a film surface temperature is lowered to eliminate a problem of specific heat capacity because as the photogravure plated rolls, there are present two types of rolls, i.e. one roll having aluminum as its base material and the other roll having iron as its base material, and additionally, their roll diameters are different from each other and different roll diameters cause their thickness to be entirely different, resulting in that even if they are heated by heater only for the same period of time in reference to a difference in specific heat capacity, heat is transmitted to the roll base materials and a film surface temperature is not always heated to 130° C. and disturbance where the rolls are heated to various different temperatures is produced.
The present inventors considered that the burning operation for substantially decreasing a concentration of solvent can be accomplished even if it is carried out under a far lower temperature than 130° C. by selecting composition showing a superior removal of solvent.
A test for reducing the heating time was carried out, a burning temperature for the film surface was decreased to 80° C. to 100° C. and the burning operation was carried out for 50 minutes, it was confirmed that a concentration of the solvent becomes 6% or less. However, this operation resulted in poor developing state. It has been concluded as its cause that the aforesaid silane-coupling agent cannot attain any requisite and sufficient adhesion.
Then, in place of silane-coupling agent acting as adherence agent, imidazole acting as hardening promoter was tried to be inputted. However, there was no specific change as for the case of silane-coupling agent and a burning temperature at the film surface was also the same as that of the silane-coupling agent.
Subsequently, the present inventors performed an experiment that various kinds of adherence agents are added against undiluted solution of the positive-type photo-sensitive composition composed of alkaline soluble organic high-molecular substance having phenolic hydroxyl group and photo-thermal converting substance for absorbing infrared rays of an image exposure light source and converting the infrared rays into heat, a photo-sensitive film is formed on the copper sulfate plating roll at a room temperature of 25° C., a test image is exposed by the aforesaid infrared laser exposure device (manufactured by Think Laboratory Co., Ltd.) to develop the film, resulting that a burning temperature for the photosensitive film of the positive-type photosensitive composition added with titanium organic compound could be remarkably decreased.
In the case of the photosensitive film of positive-type photosensitive composition added with titanium organic compound, the film could be made in a superior manner even at a burning temperature of 46° C., its sensitivity became superior and developing operation could be easily carried out.
However, a test not performing any burning operation could not attain any superior film formation and a poor developing occurred.
Even if the burning temperature could be decreased approximately to 50° C., it became a disadvantage in reference to a necessity of performing the burning operation, a necessity of performing a cooling operation after burning operation, taking time and energy for the burning operation and its subsequent cooling operation, an extended length of a device line by a length of the burning device, an increased facility expenditure and an increased running cost. Thus, the present inventors considered that an elimination of the burning operation is a problem to be solved.
Performing a burning operation shows that the roll has a high thermal load differing from that of a thin plate member, it takes 30 to 60 minutes for being heated to a requisite temperature, it takes 50 to 100 minutes or longer for being cooled down to a room temperature and further a uniform control cannot be carried out because these times are made different in reference to a size of the roll. In addition, performing the burning operation causes the cyanine pigment to be denatured, its sensitivity to be decreased, a clear pattern to be deteriorated, a thickness of the resist to be thinned at the time of developing operation, its contour to be retracted and a cause of producing some pinholes to be generated.
Accordingly, a development of the positive-type photosensitive film not requiring any burning operation has been highly desired.
As a result of repetition of tests performed by several times, a high total concentration of residual solvent such as MEK, IPA, PM and the like at the time of making a film clarified that an image cannot be printed by a laser (either a principal chain or a side chain of molecules of photosensitive film forming resin at the exposed part is cut to cause them to become low molecules showing a more increased alkaline solubility and at the same time, a latent image under a state where the photosensitive layer is properly dispersed cannot be formed).
A residual concentration of solvent when the positive-type photosensitive agent was coated on the copper sulfate plating plate and upon elapsing of 15 minutes under a natural drying condition where no air blowing was carried out at a room temperature of 25° C. was 11%, and a residual concentration of solvent upon elapsing of 25 hours was 9%. Result of measurement upon elapsing of 10 minutes in which the positive-type photosensitive agent was coated on the photogravure plated roll rotated at 45 r.p.m. showed that a residual concentration of the solvent was merely decreased down to 7%.
Accordingly, in order to modify quality by containing promoter enforcing adherence power in the positive-type photosensitive agent, remake undiluted solution of the positive-type photosensitive film not requiring any burning operation and confirm its result through exposure and developing, it has been found apparent that it is necessary to devise in advance a technology capable of substantially reducing a residual concentration of solvent in compliance with the foregoing.
Then, the present inventors et al., for the first time set, as a theme of development, a practical application of the positive-type photosensitive film not requiring any burning operation, discriminated as a technical concept, both developments, i.e. one development of a film making and drying technology capable of substantially reducing a residual concentration of solvent in a short period of time and easily by another means not dependent on the burning operation after film formation, and the other development of the positive-type photosensitive film capable of substantially improving an adherence characteristic of the positive-type photosensitive film itself through adding of promoter strengthening the adherence power and showing a high developing latitude, and then continued the study so as to solve the former problem at first.
The present inventors have considered the fact that solvent volatilizes from the coated film. It is considered that a dispersion characteristic of the solvent present at the inner layer is decreased as the time elapses and the surface is dried more and more because the coated film contacts air to dry from its surface and increase its hardness and its tissue is fastened. In turn, it is considered that a degree in which the solvent volatilizes from the coated film is made different by a pressure of surrounding atmosphere, a degree of volatilization where the solvent volatilizes from the coated film is high under a negative pressure and the residual solvent can be effectively reduced. However, it is not possible to place the roll having a film coated thereon in a room vacuumed by a vacuum pump.
In view of the foregoing, the present inventors et al. rotated the photogravure plated roll at a high speed after no liquid dripping at the coated film and found that a residual concentration of the solvent can be decreased to 3% or less within a short period of time.
In view of the foregoing, the photogravure plated roll was supported at both ends in a horizontal state in the photosensitive film coating device in accordance with Japanese Patent Publication No. 1995(7)-109511, rotated at a predetermined low speed, test photosensitive liquid was uniformly coated by a spiral scan and non-contact coating system, the rotation was continued after this operation, the photosensitive film with such a degree of drying as one in which the solvent is volatilized not to cause any liquid dripping was set.
Subsequently, as a technology capable of substantially decreasing a concentration of solvent within a quite short period of time without performing any burning operation, the present inventors et al. have established a technology for attaining a formed film having a lower residual concentration of solvent capable of realizing an image printing characteristic with laser beam while the residual solvent in the film is dispersed and removed into air by rotating the photogravure plated roll at a predetermined high speed for a predetermined time, acting a centrifugal force against the residual solvent in the film and frictionally contacting the film surface with air.
Photosensitive liquid was uniformly coated on a test roll of φ 200 mm, its rotation was continued at 25 r.p.m. for 5 minutes upon completion of coating operation, and after this, the rotation was stopped, it was waited for 5 minutes, liquid dripping was observed, no liquid dripping was confirmed by naked eyes, the test roll was rotated at 100 r.p.m. for 20 minutes and stopped, a residual concentration of solvent in the photosensitive film was measured and its value was 2.3%.
Further, the technology capable of substantially decreasing the concentration of solvent within a quite short period of time without performing any burning operation has been developed, resulting in that the promoter for enforcing various kinds of adherence power was added, the positive-type photosensitive agent was exposed and developed and a study was continued whether or not the agent has a developing latitude.
As a result, titanium organic compound of at least one of cellulose derivative, titanium alkoxide, titanium acrylate, or titanium chelate was included in undiluted solution of positive-type photosensitive composition composed of alkaline soluble organic high-molecular substance having phenolic hydroxyl group and photo-thermal conversion substance for absorbing infrared rays of the image exposure light source and tested, resulting in that a burning processing caused a poor developing operation, no burning operation caused a superior developing state and the most superior resist pattern could be attained. At this time, a room temperature was 25 to 27° C. and a humidity was about 50 to 55%.
However, test carried out at a day having the highest air temperature of about 16° C. and a quite low humidity of 21 to 23% showed that the photosensitive film was entirely removed through developing operation.
It is known in the industry in general that the positive-type photosensitive agent has a humidity dependency in which it may generate a whitening phenomenon at a high humidity of 60% or more and a film cannot be formed.
However, the aforesaid result clarified that an adherence power of the positive-type photosensitive agent does not appear even under a low air temperature and a quite low humidity. Further, a reason why the whitening phenomenon is generated and a film cannot be formed could not be resolved.
Thus, a dehumidifier and a humidifier were installed in a casing of a photosensitive film coating device according to the aforesaid Japanese Patent Publication No. 1995(7)-109511 so as to control a humidity, subsequently, material for enforcing an adherence power more was completely searched, a small amount of material was added to form a film and a test for exposing and developing the film was carried out in sequence, resulting in that each of the positive-type photosensitive agents in which any of adherence characteristic reforming agents of                (1) polyvinyl/polypyrrolidone/polyvinylacetate copolymers        (2) polyvinylbutyral        (3) styrene/maleic acid copolymers        (4) vinylpyrolidone/dimetylaminoetylmethacrylate copolymers        (5) terpolymer of vinylpyrrolidone/caprolactam/dimetylaminoetylmethacrylate        (6) terpenephenolic resin        (7) alkylphenolic resin        (8) polyvinylformar resin        (9) melamine/formaldehyde resin        (10) polyvinyl acetate, and        (11) ketone resinis mixed with and added with undiluted solution of alkaline soluble organic high molecular substance including epoxy resin having phenolic hydroxyl group or reacted with phenolic hydroxyl group and photo-thermal conversion substance for absorbing infrared rays of an image exposing light source and converting it into heat showed a high developing latitude.        
Describing it in detail, the photogravure plated roll of φ200 mm plated with copper sulfate was supported at both ends at a photosensitive film coating device and rotated at 25 r.p.m. under a condition in which a room temperature in an experiment room was 25° C. and a humidity in the casing of the photosensitive film coating device was changed to 25%, 30%, 55% and 60%, respectively, the roll was wiped off with a wiping cloth, the positive-type photosensitive agent was correspondingly coated, and also after completion of coating operation, the rotation was continued to prevent liquid dripping from being carried out, the film was formed upon elapsing of 5 minutes under a natural drying condition, and then the roll was rotated at 100 r.p.m. for 10 minutes, the residual solvent was reduced and its rotation was stopped.
All the photogravure-plated rolls taken out of the photosensitive film-coating device could be attained as tested rolls having luster, coated and formed with a quite hard photosensitive film showing luster and having quite high adherence power.
Film thickness of the resist was about 3.5 to 3.8 μm. Measurement of a residual concentration of solvent showed that all the test rolls showed about 2.3%.
Then, the test image was exposed (the image lines were exposed) with a laser of infrared wavelength range by the aforesaid infrared laser-exposing device (manufactured by Think Laboratory Co., Ltd.), then it was developed with alkali, resulting in that non-image line part generated a film reduction dissolved out. However, in all the cases, a quite sharp resist pattern having no residues was attained when it was immersed in the alkali developing liquid for 60 to 70 seconds. Then, it could be confirmed that the resist pattern naturally dried after elapsing a certain time upon developing action is quite hard. A film thickness of the resist film after developing operation was about 1.8 to 2.5 μm. No pinholes caused by the film reduction were generated.
With the foregoing, the present invention has been developed.